This invention relates to clinical observation and recording of eye motion and velocity, and more particularly to apparatus and methods for adapting conventional electroencephalograph (EEG) machines to record nystagmus.
Nystagmus is the involuntary, rhythmic motion of the eye caused by certain pathological conditions. Studies of nystagmus have indicated certain qualitative and quantitative factors are adequately clinically characteristic of nystagmus. For example, with respect to spontaneous nystagmus, the qualitative parameters include eye direction, rhythm, and form, and the quantitative parameters include amplitude, frequency and speed. Further, the clinical utility of observing nystagmus extends not only to the recording and study of spontaneous nystagmus, but also of induced nystagmus induced by caloric, rotary, and the like stimuli. Such induced nystagmus may be characterized by further significant clinical parameters, such as total amplitude, total number of beats, and duration.
Increasingly, the recording and study of significant parameters relating to spontaneous and induced nystagmus is being utilized as a diagnostic aid. Moreover, such utility is being found not only by specialists dealing with the eyes and proximately related areas, but also in the fields of neurology and otology. That is, it has been found that the parameters associated with spontaneous and induced nystagmus are linked to pathological factors of considerable clinical variety, including for example neck whiplash injuries, diverse injuries of the brain and skull, otological maladies, and the like.
Accordingly, the measurement and study of nystagmus is a clinical tool of widespread utility. Historically, nystagmography has evolved technically utilizing various arts. Early on, mechanical systems of levers and the like were utilized, but successful developments have tended to revolve around optical and electrical methods, and such are the techniques conventionally used today.
The electrical methods, commonly known as electronystagmography (ENG), are based on the proposition that the eyeball is charged, and behaves as an electrical dipole. Motion of the eyeball produces a varying voltage on the surrounding skin, which is nearly proportional to the position of the eye. Accordingly, electrodes may be placed in electrical contact with that skin area, sensing voltage changes and thereby producing an electrical signal representative of the eye motion. Such electrical signals correspond quite accurately to the critical clinical parameters relating to nystagmus. An extensive exposition of electronystagmography, including its technical and clinical aspects, and an index of neurological, otological, and ophthalmological cases, may be found in "Electronystagmography-Technical Aspects and Atlas" by Joseph U. Toglia, M.D., C.C. Thomas, Springfield, Illinois (1976).
Perhaps the greatest limitation to the continuing increase of clinical use, and development of further clinical methods and applications of electronystagmography, is the considerable expense associated with acquisition of ENG machines. Hence, the simple economics of machine cost versus expected frequency of use tend to dictate which practitioners and/or hospitals acquire ENG machinery. More often than not, practitioners who sometimes would find ENG analysis to be quite clinically useful, cannot justify the expense of acquiring an ENG recorder simply because of the relative infrequency of such occasions. This is particularly true for practitioners such as neurologists.
It is a primary object of the present invention to provide relatively inexpensive ENG apparatus whereby electronystagmographic diagnostic techniques may be economically extended to many practitioners who cannot presently justify the expense of ENG machinery.
While the incidence of ENG machinery is relatively uncommon with respect to the number of practitioners who might find them useful, the incidence of EEG machines is considerably greater. Further, EEG machines constitute a virtually essential tool of many practitioners for whom ENG machines are a useful but economically unjustified facility.
It is a primary object of the present invention to provide apparatus and methods for adapting EEG recorders to perform the ENG functions.
It is a further object of the present invention that the apparatus affording such adaptation function be compact and inexpensive, whereby EEG machines may be unobtrusively and conveniently adapted to record ENG functions.
It is a still further object that the adaptation apparatus in accordance with the present invention function in conjunction with conventional EEG machines on essentially a "black box" basis, whereby the adapter unit simply plugs into the input of the conventional EEG recorder, and utilizes conventional probe electrodes on the patient.
In accordance with yet another object of the present invention, it is essential that the patient be at all times protected from the electrical potentials and signals utilized in the ENG/EEG process, not only to avoid dangers from electrical shock and the like, but also to avoid spurious feedback signals which would impair the accuracy of the ENG record.